i) Field of the Invention
The present invention relates to a plastic processing method for subjecting a tip end of a metal rod material to a processing for gradually reducing a sectional area of the metal rod material.
ii) Description of Related Art
Examples of a product processed such that a sectional area of a metal rod material gradually decreases toward a tip end of the material include a minus driver, a drill such as a triangular drill, and the like.
As a conventional method for processing the tip end of the minus driver, a method shown in FIG. 12 is known. According to the method, first as shown in FIG. 12A a metal rod material 3 as a raw material is cut to a desired length, and next as shown in FIG. 12B a tip end 21 is press molded to be flat. After the press molding, as shown in FIGS. 12C, 12D, side surfaces 21a, 21b of the tip end 21 and a tip end shape 22 are ground in order, and a shape of the minus driver is formed. Subsequently, a burr generated during the grinding is removed by barrel grinding or the like, and the material is chamfered, so that a minus driver 6 is obtained as shown in FIG. 12E. In the minus driver 6 shown in FIG. 12E, by the aforementioned processing, the tip end of the metal rod material 3 has a flat and tapered tip end shape 5a whose sectional area gradually decreases.
Moreover, as a conventional method for processing the tip end of the triangular drill, a method shown in perspective and surface views of FIG. 13 is known. According to the method, first as shown in FIG. 13A the metal rod material 3 as the raw material is cut to the desired length. Subsequently, as shown in FIG. 13B the tip end is ground to form a conical tip end 23, and next as shown in FIG. 13C the conical tip end 23 is press molded to form a triangular pyramid tip end 24 of the material. After the press molding, as shown in FIGS. 13D, 13E, first, second and third surfaces 24a, 24b, 24c of the triangular pyramid tip end 24 are ground in order, and a tip end shape of the triangular drill is formed. Subsequently, the burr generated during cutting is removed by electrolytic grinding, chemical grinding, and the like, and a cutting edge is used, so that a triangular drill 13 is obtained as shown in FIG. 13F. In the triangular drill 13 shown in FIG. 13F, by the aforementioned processing, the tip end of the metal rod material 3 has a sharp triangular pyramid tip end shape 5b whose sectional area gradually decreases.
However, according to the conventional processing methods, a large number of steps are required until the tip ends of the minus driver 6 and triangular drill 13 are shaped. Therefore, the methods are disadvantageously intricate.
The present invention has been developed to solve the aforementioned problem, and an object thereof is to provide a plastic processing method for easily shaping a tip end of a metal rod material whose sectional area gradually decreases.
To achieve the object, according to the present invention, there is provided a plastic processing method of a metal rod material, comprising the steps of: containing the rod material in a molding groove which is disposed in a mold for molding the metal rod material and which has at least one end having a sectional area smaller than the sectional area of the rod material along a longitudinal direction of the rod material; pressing a rolling roller in contact with a mold surface having the molding groove, rolling/moving the rolling roller toward the end having the sectional area smaller than the sectional area of the rod material from the other end of the molding groove, and plastically deforming and molding the rod material along a shape of the molding groove by the rolling roller; and removing a burr formed of an excess material extruded out of the molding groove by the rolling roller during the plastic deformation.
According to the plastic processing method of the present invention, first the metal rod material as a raw material is contained in the molding groove of the mold. Any metal rod material can be used as long as the material has plasticity, but materials having no plasticity such as a cast material, sintered material and hardened material are inappropriate.
Subsequently, the rolling roller is pressed in contact with the surface of the mold in which the metal rod material is contained in the molding groove, and rolled/moved toward the end having a sectional area smaller than that of the rod material from the other end of the molding groove. Then, with movement of the rolling roller, the metal rod material is pressed onto the molding groove by the rolling roller, plastically deformed along the molding groove, and molded in accordance with the shape of the molding groove.
In this case, the sectional area of the molding groove is smaller than the sectional area of the metal rod material in at least one end along the longitudinal direction of the metal rod material. Then, the excess material of the metal rod material overflowing from the molding groove is extruded out of the molding groove by the rolling roller, and rolled between the mold and the rolling roller, and a foil-shaped burr is formed.
Subsequent to the plastic deformation, the burr is removed, and the metal rod material having the tip end shaped along the molding groove can be obtained. To remove the burr, barrel grinding is suitable when the tip end of the material shaped along the molding groove needs to be chamfered. Moreover, when a cutting edge needs to be used for the tip end, electrolytic grinding, chemical grinding, and the like are suitable for removing the burr.
According to a plastic deforming method of the present invention, by a simple operation of containing the metal rod material in the molding groove disposed in the mold and pressing and rolling the rolling roller on the surface of the mold, the tip end of the metal rod material can obtain the shape whose sectional area gradually decreases. Therefore, the metal rod material having the tip end shaped as described above can easily be molded.
According to the plastic deforming method of the present invention, the molding groove has a sectional area smaller than the sectional area of the rod material on a tip-end side along the longitudinal direction of the rod material, has a width and depth larger in size than a diameter of the rod material on a rear-end side, and has a sectional area gradually decreasing toward the tip end thereof on the tip-end side. In a portion having the width and depth larger in size than the diameter of the metal rod material on the rear-end side of the molding groove, the metal rod material is completely contained in the molding groove. Moreover, when the rolling roller is pressed and rolled onto the mold surface in a portion having the sectional area smaller than the sectional area of the metal rod material on the tip-end side of the molding groove, the rod material can plastically be processed without any difficulty. Therefore, a mold damage, particularly a damage of the molding groove can be prevented. Moreover, since the sectional area of the molding groove gradually decreases toward the tip end on the tip-end side, the metal rod material can smoothly and plastically be deformed along the molding groove.
In the plastic deforming method of the present invention, the rolling roller is rotated together with a roller having a diameter larger than a diameter of the rolling roller, pressed in contact with the mold surface by the large-diameter roller, and therefore protected by the large-diameter roller and prevented from being damaged.
Moreover, the rolling roller rotates together with the large-diameter roller, and a plurality of rolling rollers are supported by a retainer ring disposed coaxially with the large-diameter roller in an outer periphery of the large-diameter roller, and arranged in a planetary shape. Therefore, even in this case, when the rolling roller is pressed in contact with the mold surface by the large-diameter roller, an action/effect similar to the aforementioned action/effect can be attained.
In the plastic deforming method of the present invention, when the mold has a relatively small sectional area decrease ratio, a large-diameter rolling roller is used. Moreover, in a mold whose sectional area decrease ratio is relatively large or which has zero section, a small-diameter rolling roller is used.